A reactor period meter is a device for monitoring a reactor's period T. With the reactor period below a critical value, that is, it is too short, the power level is increasing too quickly. A reactor scram signal should be initiated by the reactor period meter, indicating the reactor power should be reduced. Such a meter includes means for developing a signal proportional to reactor period and logical elements for determining whether the reactor period indicated by the signal is at a critical scram level. For use in a reactor period meter, such logic elements should be fail safe, and should indicate scram condition with the reactor period at the scram level and it should indicate scram condition with failure of any of the components of the period meter. With D.C. digital, logical elements, failure of the logic elements themselves might not necessarily cause a scram signal to be generated by the meter. Thus, constant checking of the meter in a nonoperational condition is required.
It is therefore an object of this invention to provide fail safe logic elements.
Another object of this invention is to provide fail safe logic elements for a reactor period meter.